The present invention relates to agriculture, and more particularly to a novel greenhouse construction which significantly enhances the capability of plant growth in a controlled environment. In general terms, the present invention is directed to a greenhouse construction in which the roof, formed of flexible material such as double ply polyethylene, is automatically retractable and closeable, from opposite sides of the greenhouse, thereby selectively permitting or inhibiting entry of direct sunlight on plants being grown within the greenhouse.
Greenhouses have been used for many years to facilitate a controlled environment for plant growth, and typically take the form of some type of framed construction having a roof which will permit some degree of penetration by the sun's rays. Plants are placed within the greenhouse and, in conventional constructions, are watered and kept at a temperature above freezing. One problem with conventional greenhouse constructions which have double ply covers is that temperature inside the greenhouse may become relatively high, i.e. in the neighborhood of 80-90 degrees during the daytime. However, at night, the temperature within the greenhouse may approach that of freezing. The result is that the plants tend to "stretch," meaning that their stems tend to elongate and become somewhat stringy, accompanied by a weak leaf system as well as weak roots. This is caused by the plants reaching for light, the stretching being promoted by the large temperature differential which may occur in the greenhouse between daytime and nighttime.
If the plants are grown in a greenhouse for later transplanting, those plants which have been deformed by stretching, as described above, provide rather poor candidates for transplanting. The stems may easily break, and weak root systems mean that the roots may not hold on to soil, and a poor transplant will result, meaning lower crop yields in a field. Preferably plants for row crops, such as celery, broccoli, brussel sprouts, cabbage, etc. come from the greenhouse with short, stocky stems and relatively thick leaves and a strong root system. However, that type of plant will not be developed in a greenhouse with a high temperature differential or "dif." Accordingly, it has been proposed to provide a greenhouse in which the cover or roof may be rolled back to allow more sunlight in during the day and also to prevent excessive heat build-up within the greenhouse during excessively hot or high solar gain days.
Conventionally, many greenhouses use a double ply polyethylene cover so that a layer of air is sandwiched between the two plies. The result is both beneficial and detrimental, namely, while heat loss is held down at night, the double ply material and insulating air barrier also decrease light during the day up to 50 percent and more. If light into the greenhouse is cut down, then poor growth results. The essential problem is to develop a greenhouse which will provide uniform growth of plants by narrowing down the temperature differential between day and night, and by also providing for sufficient sunlight and maintaining growth-enhancing nighttime temperatures.
Moreover, conventional greenhouses used in agricultural operations may provide watering or irrigation by means of complex, expensive and multi component systems. These include assemblies in which there is a boom extending widthwise of the greenhouse and positioned above the growing plants. The boom is provided with a plurality of nozzles, and there is usually some type of motorized system for hauling the boom lengthwise for spraying the plants. Such a system not only has high initial construction costs, but also maintenance is expensive because of breakdowns and repairs.
It has been proposed to roll back the roof of a greenhouse to permit increased light, with one example being disclosed in Koziol (U.S. Pat. No. 3,812,616). In that patent, a small, portable greenhouse is provided in which a roll up bar is positioned along the sides, and is connected to a flexible cover so that it may be manually rolled up into a retracted position to increase the sunlight. Conversely, the roll up bar may be rolled downwardly so that the greenhouse is covered. Another example of a greenhouse, this time a larger type for agricultural purposes, is disclosed in Nagoya (U.S. Pat. No. 4,348,833). There a mechanism is provided for rolling up, to a certain extent, the roof portion of the greenhouse cover. However, the activating mechanism consists of a cumbersome motor/flexible driving shaft for connection to a roll up bar. The result is a rather complicated system and one which does not appear to be practical for wide spread agricultural use.
With the above problems inherit in conventional greenhouse designs in mind, it is a principal object of the present invention to provide a greenhouse for providing improved growth and environmental control to growing plants which includes a frame means defining a structure having a given length and width which forms a bounded, interior region for receiving plants, wherein a flexible cover means positionable over the frame means provides a roof enclosure for the structure, and elongate roller means substantially extending along the length of the structure is secured to a lengthwise edge of the cover means so that a power driven means coupled to the roller means is operable for selective, bi-directional rotation of the roller means about its longitudinal axis to extend or retract the cover means relative to the structure. The result is a greenhouse in which a vastly simplified arrangement is provided to either roll upwardly or downwardly the cover means, inasmuch as the power driven means or motor actually travels with the roller means. Thus, complicated transmissions and drives are not required, and selected openings are presented to allow direct sunlight into the greenhouse.
Another object of the present invention is to provide a greenhouse in which a positive clamping or retaining means is provided adjacent to the side of the greenhouse for engaging and firmly holding the roller means when the power driven means has displaced the roller means and the cover means into its fully extended or closed position.
Still another object of the present invention is to provide a tensioning means, such as a tension cord or the like, which is secured adjacent an end edge of the cover means for urging the ends of the cover means outwardly thereby to ensure that the cover means is fully extended lengthwise of the greenhouse.
It is still another object of the present invention to provide a novel tether means for tethering the power driven means into the ground or the structure itself so that during operation of the power driven means, it will follow along the structure during extension or retraction of the cover means.
Yet a further object of the present invention is to provide a greenhouse which includes a liquid distribution means for irrigation or other spray defined by an elongate, nozzled conduit means extending longitudinally of the greenhouse substantially centrally thereof and above the growing plants. A power drive or oscillating means is selectively actuated to rotate the conduit means through an arc so that water transferred into the conduit means is dispensed over a preselected range to ensure complete irrigation of the plants. In addition, a timing mechanism is provided so that plants adjacent the outer sides of the greenhouse will be subjected to a longer watering or irrigating sequence to ensure that they receive the same amount of water as plants which are disposed more directly beneath the conduit means.
These and additional objects and advantages of the present invention will be more readily understood after a consideration of the brief description of the drawings and the following detailed description of the preferred embodiment.